This relates generally to imaging systems, and more particularly, imaging systems that can perform continuous autofocus functions.
Modern electronic devices such as cellular telephones, cameras, and computers often use digital image sensors. Imagers (i.e., image sensors) may be formed from a two-dimensional array of image sensing pixels. Each pixel receives incident photons (light) and converts the photons into electrical signals. Image sensors are sometimes designed to provide images to electronic devices using a Joint Photographic Experts Group (JPEG) format. Imagers may calculate automatic exposure values (sometimes referred to herein as auto exposure values or auto exposure metrics) for automatically configuring exposure settings (e.g., the amount of time that the image sensing pixels receive incident light) for capturing images.
An imaging system may include an adjustable lens for focusing light onto an array of image sensing pixels. Imaging systems with an adjustable focal lens may use autofocus (AF) algorithms to configure the adjustable focal lens for optimal image sharpness.
The imaging system may perform autofocus functions to determine an optimum lens configuration for a given image scene. The autofocus functions may be performed in response to a manual trigger or performed continuously. Autofocus (AF) procedures performed continuously (sometimes referred to herein as continuous autofocus) may re-focus the lens to accommodate change in a scene being captured. For example, a video imaging system that performs continuous autofocus may re-focus a lens to accommodate movement of an object within the view of the video imaging system (i.e., movement of an object across frames captured by the video imaging system).
Performing continuous autofocus functions may cause an imaging system to consume large amounts of power. For example, re-focusing a lens consumes power associated with mechanically adjusting the lens. Autofocus functions in conventional imagers are sensitive to minor variations in a given image scene and perform excessive lens refocusing procedures (e.g., when a minor variation in the given scene should not require the lens to be refocused). Therefore it would be desirable to design an imaging system that performs improved autofocus functions.